code: def test_source_change(erepo_dir):
      url = os.fspath(erepo_dir)
      with external_repo(url) as repo:
          old_rev = repo.scm.get_rev()
  
      erepo_dir.scm_gen("file", "text", commit="a change")
  
      with external_repo(url) as repo:
          new_rev = repo.scm.get_rev()
  
      assert old_rev != new_rev
  
file_path: dvc/tests/func/test_external_repo.py
imports: import os
  from dvc.repo.open_repo import CLONES
  from dvc.repo.open_repo import _external_repo
  from dvc.scm import Git
  from dvc.testing.tmp_dir import make_subrepo
  from dvc.utils import relpath
  from dvc.utils.fs import remove
  from dvc_data.hashfile.build import build
  from dvc_data.hashfile.transfer import transfer
label_desc: Use image node_id 2 for calling a global function with example usage: test_source_change(erepo_dir) without return types